VANET自适应门限MAC层退避算法研究

车辆自组织网络(VANET)为车辆提供公平、高效的数据传输。针对密集高速移动场景,提出一种自适应门限的指数增加线性减小MAC层退避算法(A-EInLD)改善其数据冲突问题,提高系统性能。通过动态记录并更新每次成功发送时窗口的平均值并与获取的邻居节点窗口值进行比较得出竞争窗口的门限值,成功发送时基于该门限值通过连接数目对数值线性减小窗口大小从而避免冲突。最后,应用二维马尔科夫链模型分析算法并通过仿真评价性能结果。     

VANET中基于碰撞概率和过期概率的自适应退避算法研究

为了提高车载自组织网络中信标消息的广播接收率,可通过建立马尔可夫链模型得出消息的碰撞概率和过期概率随最小竞争窗口的变化关系。根据上述结论提出一种根据当前车载网中过期消息数与预先设定门限值的相对大小关系而进行最小竞争窗口调整的退避算法CEB;对新提出的算法和原有的退避算法RBEB及BEB进行了仿真对比分析。仿真结果表明,所提出的退避算法相比于已有的退避算法,信标消息性能有了很大的提升。     

基于优先级的双重退避MAC协议研究

为了更好地解决现有MAC在高负载下性能急剧下降的问题，并满足不同用户的接入需求，文章在DSCR算法基础上，提出了一种基于优先级的双重退避MAC协议。仿真结果表明，该算法能有效保证用户优先级，并大幅提高系统吞吐量，高负载下仍能保持较好的系统性能。     

HFC网络MAC协议的冲突化解算法分析与改进

对HFC网络MAC协议注过程中的几种竞争冲突的化解算法进行分析，并提出了一种自适应P坚持算法，实验表明该算法的性能比其他可实现算法更好。     

无线网络预约退避算法的实现和分析

针对无线局域网IEEE 802.11MAC层二进制退避算法的不足,当前已经提出多种典型退避算法。主要针对预约发送类退避算法进行研究分析,并提出与EBA不同的实现措施,对NS2网络仿真软件的Mac802.11模块进行了修改和扩展,实现了NS2对改进的预约退避算法的实现。结果表明,与标准DCF相比,改进的预约退避算法也能对IEEE802.11无线局域网的吞吐量、时延等方面性能有所改善。为今后基于NS2对预约退避算法的进一步开发研究奠定基础。     

一种新的以太网冲突仲裁算法

以太网技术以其算法简单、成熟、成本低、低载性能良好等优点成为当前应用最为广泛、最有前途的一种网络技术。然而标准以太网中冲突退避仲裁算法所具有的捕获效应带来的延迟抖动,使得它无法从容面对日益发展壮大的多媒体应用。如何解决延迟抖动问题已成为一个新的研究课题。它的解决将使千兆以太网的地位更上一层楼。该文提出一种新的自适应仲裁算法ABEB,旨在解决捕获效应,提高以太网应用于多媒体业务时的性能。     

适于无线多媒体传感器网络的MAC层退避算法

提出了服务区分动态退避算法--SDDB算法,通过对优先级不同的业务采用不同的退避方式,能在不显著降低网络吞吐量的同时,实现合理退避及业务优先级区分服务,有效避免二次冲突,支持突发业务流传输,保障优先级高的业务的实时传输要求,更适合多种业务并存的无线多媒体传感器网络.     

一种最小竞争窗口自适应调整的802.11退避算法

该文在对原有的IEEE 802.11 DCF研究的基础上,提出了一种基于最小竞争窗口自适应调整的退避算法(Minimum Contention Window Self-adaptive Adjusting, MCWSA)。该算法的思想是每个站点根据网络中当前的时隙利用率和理论上最优时隙利用率进行比较,周期性动态调整自身的最小竞争窗口,以适应不同的网络拥塞状况。仿真表明,该算法提高了IEEE 802.11局域网在拥塞情况下的性能,在饱和吞吐量和时延上都有不同程度的改善。     

基于多门限估计节点个数的自适应退避算法

针对现有接入协议的性能随着WLAN中节点个数增加而显著下降的问题,本文提出一种新的基于多门限估计激活节点个数的自适应退避算法.该算法优化了时延模型,针对最优退避竞争窗口,分析给出了竞争窗口是激活节点数目的线性函数以及准确的窗系数计算方法;通过更公平地计算空闲时隙间隔,使用三个门限来识别节点个数变化的四种情况,实现了节点个数的估计.理论分析表明,该退避算法使得碰撞概率较小并能获得较高的总吞吐量,同时节点个数的变化对性能影响较小.仿真验证了分析的正确性和算法较好的可扩展性,在公平性方面也优于其它算法.     

基于网络拥塞程度阈值的退避算法

对IEEE802.11无线网络MAC层技术所使用的DCF协议退避算法进行了分析,针对二进制指数退避算法BEB存在的不足,改进了从平均退避窗口取阈值的方案,基于这个阈值提出了适合Aol Hoc网络的NCT退避算法.OPNET仿真结果表明,改进的退避算法能提高网络吞吐量,改善网络性能.     

Design of MAC protocols with fast collision resolution for wireless local area networks

Development of efficient medium access control (MAC) protocols providing both high throughput performance for data traffic and good quality of service (QoS) support for real-time traffic is the current major focus in distributed contention-based MAC protocol research. In this paper, we propose an efficient contention resolution algorithm for wireless local area networks, namely, the fast collision resolution (FCR) algorithm. The MAC protocol with this new algorithm attempts to provide significantly higher throughput performance for data services than the IEEE 802.11 MAC algorithm and more advanced dynamic tuning backoff (DTB) algorithm. We demonstrate that this algorithm indeed resolves collisions faster and reduces the idle slots more effectively. To provide good fairness performance and to support good QoS for real-time traffic, we incorporate the self-clocked fair queueing algorithm and a priority scheme into the FCR algorithm and come up with the real-time FCR (RT-FCR) algorithm, and show that RT-FCR can simultaneously achieve high throughput and good fairness performance for nonreal-time traffic while maintaining satisfactory QoS support for real-time traffic.     

基于节能策略的无线传感器网络MAC协议

由于无线传感器网络的特殊性,针对其节能问题的媒体访问控制(MAC)协议研究越来越受到人们的关注.首先分析了无线传感器网络中能源损耗的原因,接着对近年来典型的基于节能策略的无线传感器网络MAC协议进行了分析总结,并综合其它性能指标比较了协议性能,最后提出了一些未来的研究方向.     

基于UWB通信系统的MAC协议研究

目前,超宽带(UWB)技术由于其特有的优点受到越来越多的关注,其中,针对于UWB系统的MAC协议的设计逐渐成为热点。与现有无线通信系统相比,UWB系统占有更宽的频带,具有更高的传输速率,发射功率谱密度非常低,因此,需要设计符合该系统特点,满足该系统节能、高吞吐量以及低时延等要求的MAC协议。文章通过对现有用于UWB通信系统的MAC协议的综合分析和比较,提出对UWB-MAC协议设计的要求。     

一种新的紫外光自组织通信网络MAC层避退算法

紫外光自组织通信网络是把紫外光与自组织网络相结合的,能够利用自组织网络的多跳特性来克服紫外光距离有限性的通信网络。为了使紫外光自组织通信网络中各个节点能够对有限的信道资源进行充分与公平的利用,需要对网络协议栈中的第二层——媒介接入控制层上的传统算法进行优化。本文以媒质接入控制层(MAC,Media Access Control)传统上采用的二进制指数退避算法为基础,以提高公平性为目的,提出了依据退避计数器值的随机选取是否合理,继而采取相应的奖励惩罚机制的新算法。研究结果表明:新算法提高了无线紫外光自组织通信网络中各节点接入信道的公平性,并在信道吞吐量和信道接入公平性之间达到了一个较好的折衷。     

Slot reuse in MAC protocols for MAN's

Most of the medium-access control (MAC) sublayer protocols recently proposed for application in very high-speed local and metropolitan area networks (LANs and MANs) are based on a slotted transmission scheme. Slotting guarantees very good throughput efficiencies, but further gains are possible if slots can be freed after reaching their destination, thus being available for repeated use as they propagate in the network. The authors describe a simulation-based quantitative analysis of the performance gains obtained by introducing slot reuse in distributed-queue dual-bus (DQDB) and cyclic reservation multiaccess (CRMA) MANs. CRMA-II, the latest evolution of CRMA, naturally incorporates slot reuse in the MAC protocol operations and is considered in the study for comparison purposes. In the case of the standard DQDB protocol, some existing proposals are considered. In the case of CRMA, both a previous IBM proposal and a novel approach, leading to very good performances, are studied     

Carrier‐sense‐assisted adaptive learning MAC protocols for distributed wireless LANs

A Carrier‐sense‐assisted adaptive learning MAC protocol for wireless LANs, capable of operating efficiently in bursty traffic wireless networks with unreliable channel feedback, is introduced. According to the proposed protocol, the mobile station that is granted permission to transmit is selected by means of learning automata. At each station, the learning automaton takes into account the network feedback information in order to update the choice probability of each mobile station. The proposed protocol utilizes carrier sensing in order to reduce the collisions that are caused by different decisions at the various mobile stations due to the unreliable channel feedback. Simulation results show satisfactory performance of the proposed protocol compared to similar MAC protocols. Copyright © 2005 John Wiley & Sons, Ltd.     

无线传感器网络及其MAC层协议

无线传感器网络（WSN）是当今信息领域的一大研究热点，在军事、环境、医疗护理和智能家居等方面有着广阔的应用前景，引起了世界各国的广泛关注。首先介绍了无线传感器网络的相关理论知识，然后对无线传感器网络目前所采用的典型的MAC协议按类型进行了介绍。     

On the implant communication and MAC protocols for WBAN

Recent advances in micro‐electro‐mechanical systems, wireless communication, low‐power intelligent sensors, and semiconductor technologies have allowed the realization of a wireless body area network (WBAN). A WBAN provides unobtrusive health monitoring for a long period of time with real‐time updates to the physician. It is widely used for ubiquitous health care, entertainment, and military applications. The implantable and wearable medical devices have several critical requirements such as power consumption, data rate, size, and low‐power medium access control (MAC) protocols. This article consists of two parts: body implant communication, which is concerned with the communication to and from a human body using radio frequency (RF) technology, and WBAN MAC protocols, which presents several low‐power MAC protocols for a WBAN with useful guidelines including a case study of IEEE 802.15.4, PB‐TDMA, and SMAC protocols. In body implant communication, the in‐body RF performance is affected considerably by the implant's depth and different polarization combinations inside the human body as well as by the muscle and fat. We observe best performance at a depth of 3 to 5 cm and not close to the human skin. Furthermore, the study of low‐power MAC protocols highlights the most important aspects of developing a novel low‐power and reliable MAC protocol for a WBAN. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessment and performance analysis of DQDB MAC protocols

Distributed queue dual bus (DQDB) has been adopted as the IEEE 802.6 standard for metropolitan area networks (MANs). The access mechanism is based on an implicit distributed queue maintained at each node. DQDB has been shown to achieve maximal aggregate throughput and minimal access delay independent of the size and speed of the network. However, as the size and load of the network increase, DQDB gives rise to throughput unfairness problems due to the long propagation delay. This paper initially presents a survey and assessment of recently proposed remedial DQDB mechanisms. These approaches are categorized as time division multiplexing (TDM)-oriented versus non-TDM-oriented, and exhaustive versus non-exhaustive operations. Regarding TDM as the most promising mechanism, the paper then provides the performance analysis of one TDM-oriented method, called multiple segment control (MSC), proposed by the authors. In the analysis, the network is modelled as a set of identicalM/G/1 queues, each with different services for transmitting the first and remaining segments in a busy period. The average aggregate access delay is then analyzed via an embedded Markov model. The paper shows simulation results to demonstrate the precision of the performance analysis and the performance superiority of MSC over non-TDM-oriented DQDB mechanisms. Furthermore, as will be shown, the network using the TDM-oriented method may incur bandwidth waste should active stations fail. The paper finally proposes a guardian reliability scheme to ensure the robustness of networks.